L-Arginine-d7 is intended for use as an internal standard for the quantification of L-arginine by GC- or LC-MS. L-Arginine is an amino acid and a precursor of nitric oxide (NO). L-Arginine is a substrate for NO synthase that is oxidized to form NO and L-citrulline. It enhances NO release induced by bradykinin or A23187 in porcine aortic endothelial cells. L-Arginine (30 and 300 mg/kg, i.v.) induces dilation of pial arterioles and increases cerebral blood flow in normotensive and spontaneously hypertensive rats. It also reduces infarct size by 35 and 28% in normotensive and spontaneously hypertensive rats, respectively, following middle cerebral artery occlusion.